Combine 3 pints of the blueberries, 1/4 cup sugar, and the water, cornstarch, cinnamon, vanilla and salt in a saucepan. Bring to a simmer and cook until the mixture is gooey and thick, 30 to 45 minutes. Remove from the heat and stir in the remaining 1 pint blueberries and the butter and lemon zest. Let cool.
In the meantime, roll out 1 disc of pie dough and place it in a 9-inch pie dish, tucking and crimping the edges. Freeze for 15 minutes.
Preheat the oven to 350 degrees F.
Place a piece of parchment paper inside the frozen pie shell and fill with beans or pie weights. Bake for 20 minutes, then remove the beans and parchment and continue baking for another 10 minutes. Let cool for 5 minutes.
Add the filling and bake until a skin forms on top of the filling. Remove from the oven and set aside.
Whisk together the egg, a heavy pinch of sugar and a splash of water in a small bowl. Roll out the second disc of pie dough and use cutters to make cut-out leaves or rosettes and vines. Brush the tops of the cut-outs with egg wash.
Top the pie with the cut-outs. Bake until the decorative pie topping is golden brown, 5 minutes.
Lower the oven temperature to 300 degrees F and continue baking for another 30 minutes. Let cool.
Yield:two 9-inch pie crusts
Add the flour, sugar and salt to the bowl of a food processor; pulse to combine. Add the butter and pulse until mealy. Put the mixture in a large mixing bowl.
Combine the water and vinegar in a small bowl. Gradually drizzle the liquid into the flour mixture and gently bring the dough together until it is homogenous--be careful not overmix. Divide the dough into two balls, press into discs and wrap tightly in plastic wrap. Chill in the refrigerator for 30 minutes.